The need for spill-proof cups, as used by infants and the infirm, is well known. These are cups with a liquid-tight, preferably also air-tight, cap and are designed not to leak when the cup is held in a tilted or overturned position by a child, or when the cup falls on its side or even turns over. Preferably, the cup should also resist spillage when shaken or swung as happens when children carry it around carelessly. Additionally, it would be desirable if the cup, when inverted or partially so, is also capable of resisting internal pressures as generated when a partially filled cup warms up, for instance in a hot car, or generally some time after having been filled with liquid colder than the ambient air. Ideally, the cup should remain spill proof even with carbonated drinks and with hot warn/hot liquids where internal pressure is created when the cup is inverted, whereupon the warm liquid heats the ullage space, which tends to expand while the outlet is already covered. Finally, a cup should be economical to produce, be easily cleanable and resistant to damage from biting.
There are various known designs that go some way towards meeting the above desiderata. A first known design requires some deliberate action to be taken to seal and/or open the cups. Such cups suffer from the obvious disadvantage that an infant cannot be relied on to operate the closure.
Other known designs include a pressure operated valve that is intended to open automatically in response to a reduced pressure in the spout, and to reseal when the suction is removed. Most such valves suffer from the general problem that they cannot distinguish between high pressure within the container and low pressure in the spout. Therefore these valves are either not efficient in blocking leaks, or else they offer an undesirable level of resistance to suction.
A further problem with cups having pressure operated valves is that they cannot safely be used with carbonated or hot beverages. In the latter case, when the cup is inverted the liquid heats the air in the ullage space and increases the pressure within the container because the outlet is already covered by the liquid that is then driven out.
A spill-proof that avoids the above disadvantages has been disclosed in WO2008/125877 which uses a valve known as a self-sealing demand valve. The “self-sealing” refers to the fact that the pressure inside the container acts to close the valve rather than to open it. An important advantage of such a valve is that it can be designed to allow the valve to be opened by a very low suction level. However, the demand valve is made up of several components that need to be fitted to one another and which have to be dismantled for cleaning.
Caps for non-spill cups made from a single resilient moulding exist but they require a hefty biting action on the spout. Apart from the fact that biting down hard on a spout or nipple does not come naturally to an infant (thankfully for breast feeding mothers), it can damage the spout and reduce the life of the cup. Despite this major problem, cups with a one-piece cap still fail to achieve some of the desirable features mentioned above. In particular, they leak if shaken, and when filled with a hot or carbonated liquid.